Future, e.g., Fifth Generation (5G), cellular communications networks are expected to be heterogeneous, ultra-dense networks and may utilize millimeter wave (mmWave) frequencies (e.g., 1 gigahertz (GHz) up to tens of GHz or above). Downlink-Uplink Decoupling (DUDe) has been recently proposed to improve User Equipment device (UE) battery lifetimes, uplink coverage (e.g., uplink Signal-to-Interference-plus-Noise Ratio (SINR)), and data rates as well as to reduce the inter-cell interference in heterogeneous, ultra-dense and/or mmWave networks. In this respect, “uplink” refers to the direction from the UE to the network, and “downlink” refers to the direction from the network to the UE. In DUDe, different non-co-located radio access nodes serve a UE for downlink traffic and uplink traffic delivery. Furthermore, in DUDe operation, typically the radio access nodes serving the UE belong to different radio access node power classes, e.g. mixture of high power radio access nodes which may also be referred to herein as macro base stations and low power radio access nodes which may also be referred to herein as pico radio access nodes. In future cellular communications networks, when implementing DUDe, downlink and uplink traffic flows may also be routed via a mixture of licensed and unlicensed carriers, requiring different allocation criteria. For example, a UE may have a first connection to a high power node operating on a licensed carrier frequency and a second connection to a low power radio access node operating on an unlicensed carrier frequency. This means typically the downlink and uplink traffic will be served by non-co-located radio access nodes via a mixture of licensed and unlicensed carriers. Therefore, it is expected that DUDe gains in future deployments will be significant.
It is also expected that deployments of future cellular communications networks will be characterized by a mixture of user-deployed and operator-deployed radio access nodes with different power levels using frequencies ranging from below 1 GHz to tens of gigahertz (mmWave). The different radio access nodes are expected to provide services for very different types of traffic and natively support Device-to-Device (D2D) communications.
Recent studies on electromagnetic field exposure show that, in order to be compliant with applicable exposure limits at frequencies above 6 GHz, the maximum transmit power in the uplink may have to be several decibels (dB) below the power levels used for current cellular technologies. Since the transmit power has an important impact on uplink coverage, in particular for sounding over a non-precoded channel, a pragmatic approach is to use DUDe where the uplink of a UE is provided via a connection with one radio access node on a lower frequency (e.g., a carrier frequency that is less than 6 GHz) with a better link budget and a downlink of the UE is provided via a connection with another radio access node on a higher carrier frequency (e.g., a carrier frequency that is greater than or equal to 6 GHz). In other words, in a mmWave network, associating a UE to a mmWave small cell in the downlink and to a sub-6-GHz macro cell in the uplink utilizing DUDe is beneficial.
As discussed above, future cellular communications networks are expected to utilize an unlicensed frequency band or a mixture of licensed and unlicensed frequency bands. In unlicensed frequency bands, transceivers using a particular part of the band must adhere to regulations on transmitted energy, duty cycle, adjacent carrier leakage, Radio Frequency (RF) spectrum emissions, and other aspects of wireless communications. Clear Channel Assessment (CCA), Carrier Sensing (CS), and Listen-Before-Talk (LBT) are mechanisms that help transmitters to comply with regulations and ensure fair access to the wireless medium. Conversely, in frequency bands licensed to a Mobile Network Operator (MNO), the radio resource owner, that is the radio access node, can schedule wireless transmissions in uplink and downlink. Scheduled transmissions provide higher throughput at high loads than LBT based medium access protocols.
Future cellular communications systems are also expected to serve various types of UEs having different power limitations and power capabilities as well as different beam-forming capabilities. In particular, future cellular communications systems are expected to serve various UE categories. With respect to UE categories, UE capabilities differ in terms of approximate supported downlink/uplink data rate, number of multi-antenna layers (in uplink/downlink), highest Modulation and Coding Scheme (MCS) (e.g., whether 64 Quadrature Amplitude Modulation (QAM) is supported), maximum transmit power, etc. For example, UE category 8 devices support eight downlink Multiple Input Multiple Output (MIMO) layers and 64 QAM, while a category 6 device supports up to four MIMO layers and 16 QAM.
With respect to power limitations, UEs can be subject to power limitations to comply with requirements on signal quality and Out-Of-Band (OOB) emissions. These power limitations can be set by setting the Maximum Power Reduction (MPR), Additional MPR (AMPR), the so called DeltaTc, and other parameters known to those skilled in the art. In particular, since Release (Rel) 10 of the Third Generation Partnership Project (3GPP) standards suite, the Power Management MPR (P-MPR) allows a UE to reduce its maximum output power when other constraints are present. For example, multi-Radio Access Technology (RAT) terminals may have to limit the Long Term Evolution (LTE) transmission power if transmissions on another RAT are taking place simultaneously. Such power restrictions may arise, for example, from regulations on a Specific Absorption Rate (SAR) of radio energy into a user's body of OOB emissions requirements that may be affected by the Inter-Modulation (IM) products of the simultaneous radio transmissions. The P-MPR is not aggregated with MPR and A-MPR, since any reduction in a UE's maximum output power for the latter factors helps to satisfy the requirements that would have necessitated P-MPR. DeltaTc is a 1.5 dB reduction in the lower limit of the maximum output power range when the signal is within 4 megahertz (MHz) of the channel edge.
With respect to UE power capabilities, regular handheld UEs may have maximum transmit power capabilities that are different than that of low-energy sensors that send measurement data to a gateway data acquisition node in the proximity of the sensor.
Multiple antenna UEs can use transmit Beamforming (BF) to boost the uplink link budget. Transmit BF at the UE side requires that the UE estimates the uplink channel, since Channel State Information at the Transmitter (CSIT) is needed at the UE to form the uplink beam. Multiple antenna UEs typically have a limited number of antennas and limited BF capabilities as compared with that of a cellular base station. UEs with two or four transmit antennas can be regarded as typical, although in future systems high end UEs can be equipped with a greater number of transmit antennas. Likewise, multiple antenna UEs can use receive BF to boost the Signal-to-Noise Ratio (SNR) and/or SINR of the received signal, minimize the mean squared error of the received data symbols, suppress interference, or some combinations of such objectives that are well known to the skilled person.
Utilizing DUDe in a mixed licensed carrier and unlicensed carrier wireless communications system present new problems that need to be addressed. In particular, such a problem could relate to mitigating problematic transmission and/or reception scenarios at the wireless device which may result from transmission and/or reception in a mixed licensed carrier and unlicensed carrier wireless communication system.